Composite nonwoven/pulp fabrics have been used for applications where a stable and fixed absorbent structure is required. The pulp provides absorbency and the network of fibers in the nonwoven provides a structure for retaining the pulp and significantly increasing the wet strength of the material. One use for these fabrics is as a wipe, particularly a wipe that is impregnated with a solution during manufacture and before use.
Composite nonwoven/pulp fabrics are conventionally made by depositing a pulp layer on top of a nonwoven web and subsequently hydroentangling the nonwoven and pulp together. The composite may also include a second nonwoven web that is placed on top of the pulp and is also hydroentangled.
In the past, it has not been possible to obtain a spunbond/pulp wipe having the softness and drapability of wipes made from viscose or a viscose blend. The present invention achieves a softness and drapability comparable to viscose wipes using a spunbond/pulp composite. The present invention has a further benefit in that the continuous fibers of the spunbond nonwoven provide considerably greater wet strength than wipes made with carded staple cellulosic fibers, particularly in the CD direction.
It is desirable for wipes to have a high loft, corresponding to improved softness. A recent improvement for enhancing the loft of nonwoven webs is the use of a hydroengorgement process. Hydroengorging is a process by which a nonwoven web, having been first thermally or ultrasonically bonded, is subsequently tenderized with water jets to improve the loft of the web while still retaining most of its distinct bond sites and consequently its original strength. Some fibers may be extricated from their bond sites resulting in increased thickness or caliper and in significant improvement in softness, hand and touch. During the hydroengorgement process, the fibers in the regions between bond sites are forced to move out of the flat plane of the original nonwoven and consequently the regions between bonds fluff up and gain loft and softness. The bulked structure thus produced has larger voids between bonds compared to the original nonwoven structure, as indicated by an increase in air permeability of the new structure by at least 15% compared to the original nonwovens structure. This hydroengorgement process is further detailed in U.S. Patent Application Publication No. 2006-0057921 A1, filed Sep. 10, 2004, which is hereby incorporated by reference.
An aspect of the present invention is to improve the loft and feel of spunbond/pulp composites by using hydroengorged spunbond webs. The improved loft provided by the hydroengorgement process allows for a spunbond/pulp composite that is comparable to a viscose wipe in softness and drapability and has an improved wet strength in both the machine and cross directions due to its use of spunbond fibers.
It is also desirable in particular applications to provide a nonwoven having a three-dimensional relief structure. Particular types of three-dimensional relief surfaces include regularly creped, irregularly creped, such as might be made by the MICREX process, and various regular patterns such as a waffle structure (such as might be made by a pair of heated rolls, one having male projections and the other having mating female depressions) or a bowl/cup structure (such as might be made by a pair of heated rolls, one having cup-like projections and the other having mating-bowl-like recesses). The waffle-like structure may also be referred to as “pyramids” and the bowl/cup design may be referred to as “cones.”
While composites of carded nonwoven and pulp have been made using hydroentanglement and a three-dimensional forming surface to rearrange the fibers therein to produce the desired relief surface, this does not work well with composites of spunbond nonwoven and pulp. The difference is that, while the short staple fibers of the carded nonwoven are easily rearranged by hydroentanglement to assume the relief structure of a three-dimensional forming surface, the continuous fibers of a spunbond nonwoven will return substantially to their original, flattened state as soon as the composite is subjected to any tension, heat and/or pressure (for example the winding used to produce a roll of composite material). This is because the continuous fibers of a spunbond web are not free to rearrange themselves to conform to the forming surface. Further, when the composite is passed through the drying unit under tension (to dry it after hydraulic treatment), the elevated temperatures encountered therein may return the composite to its original flattened state.
Once pulp has been added to the nonwoven web or webs to form the composite fabric of spunbond and pulp, it is also generally undesirable to provide the entire composite with a three-dimensional relief structure (for example, by creping) because the additional mechanical stress may cause disintegration of the fabric structure and/or an uneconomical loss of pulp from the composite fabric.
An aspect of the present invention overcomes the aforementioned problems in forming a spunbond/pulp composite with a three-dimensional relief structure by creating a heat set three-dimensional relief structure in the spunbond nonwoven prior to formation and hydroentanglement of the composite.
The hydraulically co-entangled combination of a nonwoven having a hydroengorged or three-dimensional heat set structure with one or more other components (i.e. pulp) results in a cotendered nonwoven structure that is both bulky and soft.